Multiplying polynomials!?

Question

Multiply: (y^3+4y^2-8)(2y-1)

I got 2y^3-y^3. Is this correct? If not, show me right answer and how you got it please!

Answer 1

Your answer  2y^3-y^3 is not currect

 

(y^3 + 4y^2 -8) (2y - 1)

y^3(2y - 1) + 4y^2 (2y - 1) - 8(2y-1)           

y^3 (2y) - y^3(1) + 4y^2 (2y) - 4y^2(1) - 8(2y) - (-8)(1)

2 y^4 - y^3 + 8y^3 - 4y^2 - 16y + 8

2 y^4 +7y^3 - 4y^2 - 16y + 8              (Add:   - y^3 + 8y^3 = 7y^3)

The answer is       2y^4 +7y^3 - 4y^2 - 16y + 8